Embodiments of the invention relate generally to the arrangement of icebreaker vessels and, in particular, to a wide beam, multi-hull icebreaker designed to open a wide track through which large commercial vessels may traverse and with an open space between the hulls through which broken ice is funneled and may be removed to keep the track clear.
Icebreaker vessels, or “icebreakers” are designed to assist large commercial vessels in winter traffic. Such assistance includes opening or maintaining passages through ice fields and ice covered waters, as while large commercial vessels are locally reinforced to operate in broken ice, the wide beam hull form and low propulsion power of typical large commercial vessels make them unsuitable to break ice. In normal operation, an icebreaker leads the way through the ice field with the commercial vessels following, single file, in the track of the icebreaker.
The design of icebreakers has changed and improved over the decades but has always retained common structural characteristics. In general, conventional icebreakers incorporate a section at the bow that differs from the typical deep V-shaped or U-shaped sections for non-icebreaking ships by reason of a cutaway bow that can ride up on top of the ice and break the ice because of its weight. Additionally, the conventional icebreakers are mono hulls designed and built to normal commercial vessel proportions regarding the beam-to-draft and length-to-beam ratios, as a wide beam monohull would require higher than normal power to break ice, have unfavorable propulsion characteristics in open water, and result in a shallow draft hull form—with it being recognized that sufficient draft is required to submerge the propeller(s) of the icebreaker and that the higher power required to break ice in a wide beam monohull would lower the efficiency thereof as propulsion efficiency is better with larger diameter, slower turning propellers as compared to smaller diameter, faster turning propellers.
While conventional icebreaker designs are suitable for opening tracks of sufficient size and quality for allowing commercial vessels to follow therethrough, it is recognized that certain drawbacks and limitations are associated with conventional icebreaker designs. First, it is recognized that the size of commercial vessels has increased dramatically in the last 50 plus years, such that the current monohull icebreaker leaves a much narrower track than these wide commercial vessels—thereby causing the “shoulder,” or full beam at the bow, to strike unbroken ice which impedes their progress and may cause structural damage. Second, it is recognized that the monohull design of conventional icebreakers results in the ice being broken thereby remaining in the track that is formed. The broken ice in the track loses its insulating snow cover and re-freezes rapidly making it difficult to maintain a track and, in certain weather conditions, the broken ice can form into small particles with little entrained water between the particles so as to form what is called “slush ice.” Slush ice is not solid but can become thick at certain conditions and at certain locations (e.g., at the entrance of a river), and the slush ice adds friction to the hull of the commercial vessels, impeding or stopping their progress. The slush ice can also clog the water inlet (sea chest) of the vessels causing the propulsion engines of the vessel to shut down for lack of cooling water.
Therefore, it is desirable to provide an icebreaker that is capable of opening a track of sufficient width to accommodate commercial vessels of increased size and width. It is further desirable for such an icebreaker to provide for the partial removal of broken ice and slush ice from the track that is formed in order to more easily keep the track open and reduce the amount of such broken/slush ice in order to reduce friction on the hull and prevent potential clogging of the water inlet of the vessel.